mm/vmstat: add events for ksm cow

Users may use ksm by calling madvise(, , MADV_MERGEABLE) when they want to
save memory, it's a tradeoff by suffering delay on ksm cow.  Users can get
to know how much memory ksm saved by reading
/sys/kernel/mm/ksm/pages_sharing, but they don't know what's the costs of
ksm cow, and this is important of some delay sensitive tasks.

So add ksm cow events to help users evaluate whether or how to use ksm.
Also update Documentation/admin-guide/mm/ksm.rst with new added events.

Link: https://lkml.kernel.org/r/20220331035616.2390805-1-yang.yang29@zte.com.cn
Signed-off-by: Yang Yang <yang.yang29@zte.com.cn>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: xu xin <xu.xin16@zte.com.cn>
Reviewed-by: Ran Xiaokai <ran.xiaokai@zte.com.cn>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Saravanan D <saravanand@fb.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst
index 97d816791acae6c1ae85115466920e799e457240..b244f0202a0360120e8ddaf271df8d72dfa97532 100644 (file)
--- a/Documentation/admin-guide/mm/ksm.rst
+++ b/Documentation/admin-guide/mm/ksm.rst
@@ -184,6 +184,24 @@ The maximum possible ``pages_sharing/pages_shared`` ratio is limited by the
 ``max_page_sharing`` tunable. To increase the ratio ``max_page_sharing`` must
 be increased accordingly.
 
+Monitoring KSM events
+=====================
+
+There are some counters in /proc/vmstat that may be used to monitor KSM events.
+KSM might help save memory, it's a tradeoff by may suffering delay on KSM COW
+or on swapping in copy. Those events could help users evaluate whether or how
+to use KSM. For example, if cow_ksm increases too fast, user may decrease the
+range of madvise(, , MADV_MERGEABLE).
+
+cow_ksm
+       is incremented every time a KSM page triggers copy on write (COW)
+       when users try to write to a KSM page, we have to make a copy.
+
+ksm_swpin_copy
+       is incremented every time a KSM page is copied when swapping in
+       note that KSM page might be copied when swapping in because do_swap_page()
+       cannot do all the locking needed to reconstitute a cross-anon_vma KSM page.
+
 --
 Izik Eidus,
 Hugh Dickins, 17 Nov 2009

diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 16a0a4fd000be0a62eaf5ac33cb66c95808dd59b..e83967e4c20ea48fe59d6ebae050ed53d133634d 100644 (file)
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -133,6 +133,9 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
                KSM_SWPIN_COPY,
 #endif
 #endif
+#ifdef CONFIG_KSM
+               COW_KSM,
+#endif
 #ifdef CONFIG_X86
                DIRECT_MAP_LEVEL2_SPLIT,
                DIRECT_MAP_LEVEL3_SPLIT,

diff --git a/mm/memory.c b/mm/memory.c
index 8895dd2f22558fc424a7881eec7f59cda42322bc..e873a61431815e130eeace9e13de3cbe93f291ef 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3331,6 +3331,10 @@ copy:
        get_page(vmf->page);
 
        pte_unmap_unlock(vmf->pte, vmf->ptl);
+#ifdef CONFIG_KSM
+       if (PageKsm(vmf->page))
+               count_vm_event(COW_KSM);
+#endif
        return wp_page_copy(vmf);
 }
 

diff --git a/mm/vmstat.c b/mm/vmstat.c
index f2d0dec1062d57fe77e55f28970656cee08c6593..b94a2e4723ff15e75197c755ac6b2dfbfaf38662 100644 (file)
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1393,6 +1393,9 @@ const char * const vmstat_text[] = {
        "ksm_swpin_copy",
 #endif
 #endif
+#ifdef CONFIG_KSM
+       "cow_ksm",
+#endif
 #ifdef CONFIG_X86
        "direct_map_level2_splits",
        "direct_map_level3_splits",